1. Field of the Invention
The present invention relates to a multi-function peripheral, a power supply apparatus, and a power supply control method in which an electrical storage device is used as an auxiliary power supply.
2. Description of the Related Art
Recently, energy saving and improvement of convenience of a digital multi-function peripheral (MFP) have been advanced in accordance with requests from the market.
In general, the digital multi-function peripheral has a scanner function, a printer function, a copy function obtained by combining the scanner function and the printer function, and the like. The digital multi-function peripheral is adapted to reduce power consumption in a sleep state in which operations of these functions are not substantially performed. Specifically, a fixing heater for a fixing device that mainly consumes large electric power is turned off in the sleep state. Operations of components on a secondary side, which are loads on a power supply circuit, for example, various boards and sensors are also limited in the same manner as this fixing heater.
An electrical storage device such as a secondary battery or an electric double layer capacitor (EDLC) may be mounted as an auxiliary power supply that increases an electric current flowing to the fixing heater in warming up the fixing device. This reduces a warm-up time required for raising the temperature of the fixing device to a predetermined fixing temperature and improves convenience.
Incidentally, the power supply circuit of the digital multi-function peripheral is usually constituted by a switching power supply. However, it is difficult to obtain satisfactory power efficiency when operations of the components on the secondary side are limited to reduce an amount of an electric current flowing from the power supply circuit to the loads. For example, it is conceivable that a power supply unit having an expanded range of a load current with which high power efficiency is maintained or a power supply unit of a two-power supply system having an output for a standard current and an output for a small current is used as a power supply circuit. However, this scheme is not practical because an innegligible increase in manufacturing cost is caused. In this connection, JP-A-2001-103678 discloses a technique for effectively using commercial power that is comparatively inexpensive in the midnight hours. In this technique, switch control for charging the secondary battery in the midnight hours when the load current decreases and outputting electric power from the secondary battery via a switching power supply (DC/AC inverter) in hours except the midnight hours when the load current increases. However, in this technique, the switch control is performed irrespective of power efficiency of the switching power supply.